Caption: Glowing neon light tube. This consists of a glass tube containing neon gas at a low pressure. Two metal electrodes are at each end of the tube. When a voltage is applied, the gas becomes ionized and begins to glow as it transmits an electric current between the electrodes. Pure neon has a red-orange glow. Different colours can be achieved by adding other noble gases such as argon or krypton. A neon lamp is more efficient than carbon filament lamps.